We may not often think about it, but our homes, schools and workplaces are kept at a suitable temperature by insulation. But what is insulation and why do homes need it?

Unless it is an old house with solid walls or it has a room built into the roof space, insulating it is relatively straight forward. Plus, insulation in walls and roofs can reduce heating costs significantly and it’s affordable and easy to do.

An uninsulated home loses approximately*:

  • 25% of its heat through the roof
  • 33% through the walls
  • 15% through the floors
  • 15% through draughts
  • 20% through the windows

*Figures will vary with different house types and construction methods

Where does insulation go in a house?

Depending on where it is being insulated, the materials are placed in different areas.


Insulation for the roof or loft usually gets placed between and over the wooden joists in the loft, unless this has been turned into a living space or room, in which case the insulation will be covered so it isn’t showing. In this case, rigid insulation boards are put between the rafters, or foam, loosely filled. Then, plasterboard is put over them and decorated to create the desired living space.


Insulating the ceiling of a room can be difficult, as the finishing must be perfect. Ceiling insulation is often completed for thermal or acoustic purposes between floors, typically in blocks of flats. To do this, a self-supporting ceiling is installed beneath the existing ceiling and insulation material is put in between (for example rock wool, fibreglass, PUR or cellulose insulation).

A flat roof which is insulated on the inside (through the ceiling of the rooms), is called a ‘cold roof’.


Walls differ in their makeup depending on when a house was built. If it was built before the 1920s then it is likely to have solid walls. Many modern buildings will have cavity walls, made up of two walls with a gap in the middle. Usually, one wall is made of brick and the other is made of concrete.

In a cavity wall, the gap between the two means air runs through, lowering the temperature in a house. Cavity wall insulation is applied by filling the gap in the wall cavity with a suitable material.

A solid wall can be just as ineffective as a cavity wall but can be insulated from the outside or inside.


Any gaps or spaces in your floor allow heat to escape, so insulation is often placed below to help them retain heat. There are two main types of floor insulation, suspended and solid floor.

Suspended floor insulation means taking up the floorboards and laying the insulation, which can be loose-fit or in a roll, between the joists. If there is a living space underneath the floor, rigid boards can be applied to the ceiling which will give added insulation to the room above.

Solid floors can be insulated with rigid boards too, but this will raise the previous floor level. That means it will be necessary to consider that doors, skirtings, and electrical sockets may have to be adjusted.

What types of insulation are there?

There’s a vast array of insulation types available today. Below, we’ll break down what types are available and what their main properties are.

Rigid Foam

Rigid foam boards are sold as sheets, then cut to size after purchase. There are three main types:

PIR/PUR Boards

They have an aluminum backing and are made from closed cells which minimise water absorption. PIR boards have a higher heat resistance, so they are safer in the event of a fire.

Phenolic Boards

Also made with closed cells to reduce water absorption. The boards are thin but have a higher R-Value, which makes them more expensive than other forms of insulation.

Expanded Polystyrene (EPS)

This is the cheapest of the three and has an open cell structure which does mean that water vapour can get through. It is made from polystyrene balls which are molded together to create a block.

Sheep’s Wool

Sheep’s wool insulation is very popular. It’s one of the most environmentally friendly choices, it doesn’t burn, and it’s easy to work with as it’s unlikely to cause any skin irritation or breathing difficulties. Sheep’s wool insulation absorbs water, reducing ventilation issues and is a good choice for soundproofing requirements.

Foam Spray

Liquid foam insulation materials can be sprayed, foamed-in-place, injected, or poured. This means insulation can be blown into walls, on attic surfaces, or under floors to insulate and reduce air leakage. The major benefit of this type of insulation is it can be put into the smallest of cavities to form an effective air barrier and it can also be used to reduce air leakage in holes and cracks, such as window and door frames.

Loose Fill

Loose-fill insulation is lightweight and a good choice if there are awkward spaces to fill. Loose fill insulation is blown into the applied area, using a blowing machine with a flexible tube that can be moved around and pointed at specific areas. For it to work effectively in a roof, you’ll need to have enough to cover a loft floor to a minimum depth of 200mm.


Concrete floor blocks are used to build home foundations and walls and if the core of the blocks isn’t filled with steel and concrete for structural reasons, they can be filled with insulation, which raises the average wall R-value. Some manufacturers incorporate polystyrene beads into concrete blocks, while others make concrete blocks that accommodate rigid foam inserts.

How do I become an insulation installer?

Working to insulate buildings might mean you are a cavity insulation installer, thermal insulation installer or damp proofer among other roles.

There are several ways you can reach these roles. You can start on your career path by studying on a college course, an apprenticeship, or apply directly to an employer for some on-the-job training, work experience, or a role if you are already qualified.